Process for the production of substituted borazoles



3,297,749 PROGESSI FORiIIHE PRODUCTION OF SUBSTITUTED BORAZOLES ElmarfiManfred Horn and Konrad Lang, both of. Leverkusen,u;Germany, assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a German corporation 1 No Drawing j ,FiledApr 24, 1962, Ser. No. 189,705

Claims priority, application Germany, Apr. 29, 1961,

F 33,818 5 Claims. (Cl. 260-551) This invention relates to a process for the production of compounds: comprising boron and nitrogen and especially is concerned with a process of preparing organically substituted. borazoles.

More particularly the invention relates to a new and improved processt-of producing borazoles represented by the, general formula where R represents a member of the group consisting of aliphatic hydrocarbon radicals, cycloaliphatic hydrocarbonzradicals, aromatic hydrocarbon radicals, substituted aromatic ,hydrocarbon racials and aralkyl hydrocarbon radicals .The borazoles are useful as intermediate prodacts, for. example; in the production of boron-containing high polymers which exhibit neutron-absorbing propertics, and :are employed as additives to propellants and lubricants.

. Thewprevious methods for preparation of N,N',N"- trisubstituted borazoles require starting materials sensitive to: air and moisture, such as, for example, boron trichlorideand lithiumalanate, or can be carried out only in1cert ain expensive solvents, such as, for example, dialkyl ethers of polyethylene glycols. Thus, for example,

U.S.M patent specification No. 2,945,882 describes the reaction of: N,N,N"-triphenyl-B,B',B"-trichloroborazole with thehextremely moisture-sensitive lithium alanate, whilst, according to Jour. Am. Chem. Soc. 76, 3303 (19,54), the reaction of B,B,B"-trichloroborazole with lithiumgborohydride takes place with the formation of .0.5 mol of diborane per mol of lithium borohydride Dibonane is not only verypoisonous, but frequently selfignitespwhen exposed to. theair. The reaction of the .N;N', f'vrtrisubstituted B,B,B"-trichloroborazoles with example according to but, this method requires, apartfrom high temperatures, ,lithiumyborohydride which is diflicult to handle on additionto diethyl ether, and only 25% of the hydride hydrogen presentin the borohydride are recovered as N, N,N- trialkyl-B,B.',B"-trihydrogen borazole, the remainder ,e scapingas gaseous hydrogen.

Briefiygdescribed, the process of the present invention United States Patent 0 3,297,749 Patented Jan. 10, 1967 comprises effecting reaction between (1) a boron compound represented by the general formula wherein R represents a member of the group consisting of aliphatic hydrocarbon radicals, cycloaliphatic hydrocarbon radicals and aromatic hydrocarbon radicals, and (2) a primary amine represented by the formula NH -R II where R is a member of the group consisting of an aliphatic hydrocarbon radical up to 18' carbon atoms, a

cycloaliphatic hydrocarbon radical, an aromatic hydrocarbon radical, a substituted aromatic hydrocarbon radical and an aralkyl hydrocarbon radical. In order to obtain a maximum yield of the N-substituted borazole, the boron compound of Formula I and the primary amine (Formula II) are employed in a molar ratio of 1 mol of the former to 1 mol of the latter and at temperature at which 2 mols of hydrogen are split oif per mol amine; preferably in a temperature range of +40 C. to C. The reaction may be effected in an inert liquid medium and in a protecting gas at atmosphere. It is carried out under anhydrous conditions.

In the case using aniline as primary amine (Formula II), on the one hand, and of triethyl amine borane on the other hand, the process according to the invention can be described by the following equation It has been further shown that the amine boranes serving as starting materials must not be used as such, but can be prepared in situ according to the Belgian patent specification No. 571,241 by the reaction of amine, borohydride and boron halide. preferably used for this purpose which bear the same substituent as the borazole to be prepared so that the preparation of N,N,N"-trisubstituted borazoles can start directly from borohydrides, boron halide, preferably in the form on an etherate, and primary aliphatic, cycloaliphatic or aromatic amines. In the case of the boron trifluoride-tetrahydrofuran addition compound the method according to the invention can be formulated, for example, as follows:

(THF=tetrahydrofuran) thus no splitting oif of diborane takes place in this case. Instread of using primary aliphatic, cycloaliphatic or aromatic amines and boron trihalides, for example, iboron trifluoride-tetrahydrofuran addition compounds, the addition compounds of boron trifluoride and primary amines can be employed directly, as described, for example in equation These amplifications ofthe process according to the invention make it possible to widen the range of the usable amines by the group of low boiling amines.

As examples for the amines usable in the process according to the invention, there may be mentioned: aliphatic amines, such as methylamine, ethylamine, n-propylamine, i-propylamine, butylamine, octylamine, dodecylarnine, hexadecylamine, stearlyamine; cycloaliphatic amines, such as cyclohexylamine and nuclearly substituted cyclohexylamines; aromatic amines, such as aniline,

monoand polyalkyl-substituted anilines, such as tolui- Primary amine boranes are dines and xylidines; monoand polyalkoxy-substituted anilines, such as ansidines and phenetidines; aryl-substituted anilines such as 2-phenyl-aniline; nuclearly substituted anilines, such as monoand polyhalogen substituted aniline, naphthylamines and nuclearly substituted naphthylamines. I

The usable boron halides possess the general formula BX in which X stands for F, Cl, Br or I. The addition compounds of the boron halides, such as for example boron trifluoride diethyl ether or boron trifluoride tetrahydrofuran may likewise be used as starting materials in. the method according to the invention.

For economic reasons, alkali metal borohydrides, especially sodium borohydride, are preferably used, but other borohydrides such as potassium, lithium or calcium borohydride are also accessible to the reaction.

. The use of solvents or suspending agents, for example others, such as tetrahydrofuran, or hydrocarbons, is advantageous but not necessary, since other solvents or suspending agents which are inert towards the reaction components can also be employed.

The process according to the invention is carried out above the decomposition temperatures of the primary amine boranes and below the decomposition temperatures of the N,N,N"-triorganosubstituted borazoles. The decomposition temperatures of primary amine boranes are described and the thermal stability of the N,N',N"-triorganosubstituted borazoles is sufficiently known from the chemical literature.

The reaction according to the invention is surprising sinceit is well known that the decomposition of primary amine boranes leads to N-monosubstituted aminoboranes which are converted into the corresponding borazoles at very high temperatures only whereby, in some cases, pressure must be used in order to prevent the dissociation of the reaction components. In contradistinction, the reaction according to the invention takes place at a little above the transformation point of the amine boranes into aminoboranes at a great speed. Therefore, a technical progress has been achieved since borazoles sensitive to temperature have been made accessible by the process according to the.

invention.

The following examples are given for the purpose of illustrating the invention.

Example 1 Example 2 185 g. of dodecylamine (:1 mol) are placed in the apparatus described above and melted. 115 g. of triethylamine'bor'ane :1 mol) are added dropwise at a sump temperature of 130 C. within 1.5 hours and the freed triethylamine is distilled off at inside temperatures of up to 150 C. After removing the remaining triethylamine under vacuum N,N',N"-tridodecyl-B,B,B"-trihydrogenborazole is obtained as residue in form of a pale-yellow colouredviscous liquid in 93.5% yield. The analysis showed 5.24% B (theoretically 5.54% B) and 6.77% N (theoretically 7.17% N).

Example 3 205 g. of finely powdered sodium borohydride (=54 mols) are suspended in 1.87 l. of dry tetrahydrofuran, and 354 g. (:6 mols) of anhydrous n -propylamine are added. 840 g. (=6 mols) of boron trifluoride-tetrahydrofuran addition compound are slowly added dropwise with stirtetrahydrofuran and the solvent distilled off under normal pressure. After fractional distillation under vacuum N, N,N"-tri(n-propyl)-B,B,B-trihydrogen borazole is obtained, as a colorless liquid in 82% yield in addition to polymeric borazoles.

Analysis.Found: 51.58% C; 11.52% H; 19.3% N; 15.2% B; 1.35% active hydrogen. Theoretically: 52.1% C; 11.6% H; 20.3% N; 15.7% B; 1.45% active hydrogen.

Example 4 142 g. (:36 mol) of sodium borohydride are suspended in 1.3 l. of dry tetrahydrofuran and 644 g. of aniline boron trifluoride addition compound (=4 mols) are added slowly Whilst stirring so that the inside temperature does not exceed about 40 C. Subsequently, the mixture is boiled under reflux for 3 hours, cooled, sodium tetrafluoroborate and the excess of sodium borohydride are filtered off, the filter residue washed several times with tetrahydrofuran and the suspending agent is distilled ofi under normal pressure. After drying under vacuum, N,N,N -triphenyl-B,B',B"-trihydrogen borazole is obtained from the residue in 87.5% yield which after recrystallization from hexane-chloroform (1:1) shows a melting point of 158 C.

Example 5 460 g. (=4 mols) of N-triethylborazane which were heated to 140 C. with stirring in an argon atmosphere are introduced into the apparatus described in Example 1. 510 g. =4 mols) of 2-chloroaniline are added dropwise within 2 hours while distilling off the triethylamine Example 6 475 g. of white crystalline N,N',N-tri-(3-chlorophenyl)- B,B,B-trihydrogen-borazole, having a melting point of IDS-106 C., corresponding to a yield of 86 percent of the theoretical are obtained from 460 g. (4'mols) of N- triethylborazane and 510 g. (4 mols) of trichloroaniline according to Example 5. After recrystallizing from ligroin the: product has a melting point of 107 C.

Example 7 According to the procedures of Examples 5 and 6 the light grey colored crystalline N,N',N"-tri-(4-chlorophenyl)-B,B',B"-trihydrogenborazole of a melting point of. 2014-205 C. is obtained in a yield of 90 percent from 460 i g. .1 (4 rnols) of N-triethylborazane and 510 g. (4

mols) of 4- chloroaniline by melting in a dropping funnel V equipped with heating means and adding dropwise the melt ofziabout 80j C. into the borazane heated to 100 C. Aftermrecrystallizing from benzene the substance has a melting point of 207 C.

Example 8 N,N?,N7frtribenzyl-B,B',B"-trihydrogen-borazole which is identified by its infra-red spectrum is obtained in form of a Wax-like substance of the melting point of 47 C. in substantially quantitative yield in a manner analogous to EXamplesS to 7 from 667 g.(5 .8 mols) of N-triethylborazane and 621 g. (5.8 mols) of benzylamine.

(THE# tetrahydrofuran) 125 lg- (3.3 mols) of finely ground sodium borohydride aresuspended in 3 litres of dry tetrahydrofuran, and 428 g. (4 molslofbenzylamine are added. 560 g. (4 mols) p of borontrifiuorideetetrahydrofuran are added dropwise up inhexane in order to remove any residue of sodium 1 tetrafiuoborate... After filtering once more the hexane is {distilled on and the borazole is dried in vacuum. Melting point 451-46 C:

1 Wclaim:

1. A H process of preparing :N,N',N"-tricyclohexyl- B,B,B"-trihydrogen borazole which comprises heating a mixture of triethylamine borane and cyclohexylamine under anhydrous conditions, a molar ratio of 1:1, to a temperature of about 120 C. at which 2 mols of hydrogen are split oif per mol of amine and recovering the N,N',N" tricyclohexyl B,B',B trihydrogenborazole thereby obtained from the reaction mixture.

2. A process of preparing N,N',N"-tridodecyl-B,B,B"- trihydrogenborazole which comprises heating a mixture of dodecylamine and triethylamine borane under anhydrous conditions, a molar ratio of 1: 1, to a temperature of from 65 C. at which 2 mols of hydrogen are split oif per mol of amine, and recovering the N,N,N-tridodecyl- B,B',B-trihydrogen-borazole thereby obtained from the reaction mixture.

3. A process "of" preparing N,N',N' -tri( n-propyl)- B,B',B"-trihydrogen borazole which comprises reacting sodium borohydride, n-propylamine and boron trifiuoridetetrahydrofuran under anhydrous conditions, a molar ratio of 1:1 (n-propylamine:boron trifluoride-tetrahydrofuran), to a temperature of about 50-65 C. and recovering the N,N',N-tri(n-propyl)-B,B,B"-trihydrogen borazole thereby formed.

4. A process of preparing N,N',N"-triphenyl-B,B,B"- trihydrogen borazole which comprises reacting sodium borohydride and aniline boron trifluoride under anhydrous conditions to a temperature of about 40 C. at which 2 mols of hydrogen are split off per mol of amine, and isolating the borazole thereby formed from the resulting reaction mixture.

5. A process of preparing N,N',N-tribenzyl-B,B',B"- trihydrogen borazole, which comprises reacting sodium borohydride benzylamine and borontrifluoride-tetrahydrofuran under anhydrous conditions, a molar ratio of 1:1 (benzylaminezboron trifiuoride-tetrahydrofuran), to a temperature of about 45 C. at which 2 mols of hydrogen are split otf per mol of amine, and isolating the borazole thereby formed from the reaction mixture.

References Cited by the Examiner UNITED STATES PATENTS 2,978,502 4/1961 English et al 260-l 3,008,988 11/1961 Winternitz et al 26055l FOREIGN PATENTS 857,176 12/ 1960 Great Britain.

OTHER REFERENCES German Auslegeschrift 1,052,406, Mar. 12, 1959. Schaeffer et a1.: J. Am. Chem. Soc., vol. 71, pp. 2143- 2145. (1949) WALTER A. MODANCE, Primary Examiner. JOHN D. RANDOLPH, Examiner. H. I. MOATZ, Assistant Examiner. 

1. A PROCESS OF PREPARING N,N'',N"-TRICYCLOHEXYLB,B'',B"-TRIHYDROGEN BORAZOLE WHICH COMPRISES HEATING A MIXTURE OF TRIETHYLAMINE BORANE AND CYCLOHEXYLAMINE UNDER ANHYDROUS CONDITIONS, A MOLAR RATIO OF 1:1, TO A TEMPERATURE OF ABOUT 120*C. AT WHICH 2 MOLS OF HYDROGEN ARE SPLIT OFF PER MOL OF AMINE AND RECOVERING THE N,N'',N" - TRICYCLOHEXYL - B,B'',B" - TRIHYDROGENBORAZOLE THEREBY OBTAINED FROM THE REACTION MIXTURE. 